This study compared the benefits of four isocaloric diets with different protein levels (18%, 23%, 29% and 35%) fed to 4 groups of sled dogs 1 month before and during the 12-week training period. Key parameters such as body weight, energy intake, PVC, haemoglobin concentration and other biochemical indicators were measured before, during at just after the training period, and maximal oxygen uptake was measures before and after the training period. The 18% protein diet couldn’t meet the metabolic requirements of these dogs during training, whereas the 35% protein diet provided a better performance as it caused an increase in plasma volume.